This invention relates generally to the production of composite metal pipes having laminated multiple walls (hereinafter referred to as double-wall pipes) and more particularly to a technique of obtaining an extremely tight and intimate union of an inner pipe and an outer pipe in the process of producing corrosion-resistant double-wall pipes such as oil well pipes.
As is known, tubular structures to be used as, for example, oil-well pipes and piping in nuclear power plants are required to possess strength to resist pressure and heat resistance, of course, and also corrosion resistance. For meeting these requirements, there has been a trend toward the use of double-wall pipes. A typical example of such pipes is that comprising an outer pipe made of carbon steel for strength and an inner pipe of stainless steel for corrosion resistance, both steel materials possessing ample heat resistance for all practical purposes. However, for preventing trouble such as cracking and implosion of these double-wall pipes, it becomes highly important that the fit between the inner and outer pipes be extremely tight.
As measures for obtaining tight fits between the laminated pipes, the thermal shrink-fit method and the pipe-expanding method have been developed and reduced to practice. In the former method, a high degree of precision in the finishing of the surfaces of the two pipes to come into mutual contact is required, and various difficulties are encountered in practical application of this method to pipes of long unit lengths and pipes of large diameter. The pipe-expanding method has a disadvantage in that the range of selection for obtaining the desired degree of fit is limited, and, moreover, the necessary equipment for carrying out this method becomes disadvantageously large.